Atomic Structure

Question 1

Atomic model over the years

Answer 1

1803 - John Dalton and the billiard ball
1904 - JJ Thompson and the Plum Pudding model
1911- Earnest Rutherford and the nuclear model
1913 - Neil Bohr and the Bohr model

Question 2

Relative mass and charge of Protons, neutrons, and electrons. Why is the term relative used?

Answer 2

Protons 1, +1
Neutrons 1, 0
Electrons 1/1840, -1
The numbers are too small therefore a relative is used.

Question 3

What are isotopes?

Answer 3

An element with the same number of protons but different numbers of neutrons.

Question 4

How do isotopes react chemically and physically?

Answer 4

Chemically they react the same because of the number of electrons in their valence.
Physically they are different as the neutrons can affect relative mass, so melting points and densities can be affected.

Question 5

What are cations and anions

Answer 5

+ -

Question 6

What is the mass spectrometer

Answer 6

It’s a machine that measures
1. Mass of an atoms and molecules
2. Ar and Mr
3. Identifies elements
4. Very accurate

Question 7

What is the definition of relative atomic mass (Ar)?

Answer 7

Average mass of 1 atom ÷ 1/12th mass of carbon-12

Question 8

What is the definition for Mr

Answer 8

Average mass of 1 molecule ÷ 1/12th mass of carbon-12

Question 9

How many stages does the mas spectrometer have and what are they?

Answer 9

4 stages
1. Ionisation
2. Acceleration
3. Ion drift
4. Detection

Question 10

How many types of Ionisation are there?

Answer 10

There are two types: Electron impact and Electron spray

Question 11

Describe the process of Electron impact?

Answer 11

1. Sample is vaporised and hit with electron gun
2. Electrons from gun knock off electrons from sample molecules
3. Molecules (sample) is now positively charged
   (usually electrons and protons are equal but knocking off one negative electron makes it positive as there are now more protons.)

Question 12

Describe the process of Electron spray?

Answer 12

1. Sample is dissolved in a solvent and high voltage is applied
2. High voltage rips off proton from solvent and attaches to the sample molecule
3. Sample is now positively charged

Question 13

Electron impact Vs Electron Spray

Answer 13

EI:
1. causes fragmentation
2. Used for low Mr compounds
3. gaseous state (loss of electrons)

ES:
1. Gentle and prevents fragmentation
2. Used for polymers and biological molecules (DNA)
3. Gaseous state (Gains proton)

Question 14

What happens in stage two of the mass spectrometer?

Answer 14

All molecules are accelerated to have the same kinetic energy.

Question 15

What happens in stage three of the mass spectrometer?

Answer 15

1. Ste off at the same time
2. Lighter ions move faster and start to separate
3. Lighter ions reach the detector first
   (Lighter ions move faster=shorter time of flight)